In many devices that include a rotating shaft, such as but not limited to electric generators, electric motors, gear boxes such as windmill gear boxes, compressors, pumps, and the like, stray voltage may build up on the rotating shaft. Apart from any stray voltages resulting from equipment that is not functioning correctly, all rotating shafts inherently generate electric fields from asymmetries in magnetic field distribution between rotor and stator, residual magnetic flux in the shaft, excitation and electrostatic charges. These stray voltages may ultimately exit the rotating shaft through structures such as the bearings supporting the rotating shaft. Over time, this can damage the bearings and/or other components of the device.
In order to prevent current flow through structures like bearings and related components, a grounding apparatus may be used to ground the rotating shaft. Such grounding apparatus may include grounding brushes, grounding straps, grounding ropes and other grounding members configured to ground the rotating shaft of the device. In maritime applications, propulsion shafts may include a grounding apparatus in order to avoid galvanic activity that can otherwise cause erosion. There is a desire to monitor the performance of the grounding apparatus to ensure that the grounding apparatus is performing correctly. There is also a desire to monitor electrical current flowing through the grounding apparatus in order to detect and diagnose potential defects or other problems within the device.